The use of Ziegler-Natta catalysts, which usually consists of compounds of Group IV-VIB metals and organometallic compounds of Groups I-IIIA of the Periodic Table of Elements, in the polymerization of olefins are widely utilized. These catalysts are known to effectively promote the polymerization of olefins in high yield possessing the desired characteristic of these polymers. However, the use of these conventional Ziegler-Natta catalyst systems are subjected to important failings. Thus, new and improved catalysts are continually being sought.
Commonly in the polymerization of .alpha.-olefins a catalyst system having a magnesium halide support is oftentimes utilized. Unfortunately, when polyolefins obtained by polymerization of alpha olefins using these catalysts are processed into molded articles, the molding apparatus processing this polymer is subjected to corrosion. This corrosion is caused by the presence of residual halide in the polymer product. More significantly, this adverse effect of corrosion is not limited to damaging just the molding apparatus. More importantly, the polymeric molded article processed by the corroded apparatus is often characterized as having undesirable aesthetic flaws.
One of the most important properties associated with a catalyst is its catalytic activity for a defined process. The activity of a catalyst is represented by the weight of product produced per unit weight of catalyst used. Accordingly, the activity of a polymerization catalyst is defined by the weight of the polymer produced per weight of catalyst. Those skilled in the art are aware that the effect of higher activity not only reduces the amount of catalyst required for the polymerization process but more importantly this translates into lower catalyst concentration in the final polymeric product. This lower concentration of catalyst in the polymeric product usually results in a higher purity product. Thus in the development and design of novel catalysts for polymerizing olefins, this property along with the effect of the catalyst on the physical properties of the polymer must be carefully considered.
One way of achieving a higher catalytic activity without negatively effecting the physical characteristics of the polymer is to introduce so-called cocatalysts or activators to the solid catalyst component during the polymerization process.
Typically, the solid catalyst component is contacted with an organoaluminum cocatalyst during the polymerization of the olefin in order to increase the amount of polymeric product.
U.S. Pat. No. 4,806,433 to Sasaki relates to a solid catalyst component containing a trivalent titanium compound, obtained by reducing a titanium compound represented by the general formula Ti(OR.sup.1).sub.n X.sub.4-n ; wherein R.sup.1 is a hydrocarbon group of 1 to 20 carbon atoms, X is a halogen atom, and n is a number satisfying 0&lt;n.ltoreq.4 with an organomagnesium compound in the presence of an alcohol compound and/or a phenol compound to obtain a solid product and then treating the solid product with a mixture of an ether compound and titanium tetrachloride. The reference also relates to a catalyst system comprised of: the solid catalyst component described above and an organoaluminum cocatalyst compound; and a process for producing an olefin polymer, which comprises homopolymerizing an olefin or copolymerizing olefins using said catalyst system.
U.S. Pat. No. 4,983,694 to Furtek relates to a process for polymerizing at least one .alpha.-olefin with a supported catalyst component prepared by contacting a solid, porous carrier having reactive OH groups with at least one liquid organomagnesium compound having the formula R.sub.n MgR.sup.1.sub.( 2-n) where R and R.sup.1 are the same or different C.sub.1 -C.sub.12 hydrocarbyl group; evaporating said liquid to produce a supported-magnesium compound in the form of a dry, free-flowing powder; and reacting the powder with at least one transition metal compound. The solid catalyst obtained is then reacted with a suitable cocatalyst during polymerization. Suitable cocatalyst include compounds of Group IB, IIA, IIB, IIIB and IVB of the Periodic Table of Elements. The reference however does not disclose using halosilane compounds as a cocatalyst component.
U.S. Pat. No. 4,250,287 to Matlack relates to a solid catalyst component useful for polymerizing 1-olefins. The catalyst component is composed of a titanium halide deposited on an anhydrous magnesium halide support and an activator component composed of a trialkylaluminum and an alkyl ester of an aromatic carboxylic acid. The productivity of said catalyst is increased by including a halosilane in the activator component.
U.S. Pat. No. 4,950,631 to Buehler et al. discloses a catalyst comprising the product formed by
(a) treating silica to remove surface hydroxyl groups; (b) contacting said treated silica with (1) a modifying compound selected from the group consisting of silicon halides, boron halides, aluminum halides, alkyl silicon halides and mixtures thereof; and (2) at least one hydrocarbon soluble magnesium-containing compound selected from the group consisting of hydrocarbyloxy magnesium, hydrocarbyloxymagnesium halides and mixtures thereof; said contacting steps (1) and (2) occurring in random order; (c) contacting the product of step (b) with at least one titanium-containing compound having the structural formula Ti(OR).sub.n X.sub.m, where R is aryl, alkyl or mixtures thereof; X is halogen; n is an integer of 1 to 4; m is 0 or an integer of 1 to 3; and the sum of m and n is 4; and (d) treating the product of step (c) with a titanium-containing compound having the structural formula TiX.sup.1.sub.p OR.sup.1.sub.q where X.sup.1 is halogen; R.sup.1 is aryl or alkyl; p is an integer of 1 to 4; q is 0 or an integer of 1 to 3; and the sum of p and q is 4, with the proviso that the titanium-containing compound of this step is not the same as the titanium-containing compound of step (c).
The catalyst prepared by Buehler is useful in polymerizing propylene. In this application, propylene is polymerized under propylene polymerization conditions in the presence of a first co-catalyst, an aluminum-containing compound, and a second co-catalyst, a silane. Buehler et al. discloses using hydrocarbylalkoxysilanes as a cocatalyst component; however, the reference does not suggest that halosilane may be used instead of hydrocarbylalkoxysilanes.
Another way of increasing catalytic activity without affecting the physical properties of the resultant polymer is to add one or more so-called modifying compounds during preparation of the solid catalyst component. These modifying compounds are known to effectively alter the morphology of the catalytic surface. These modifying compounds are typically added during the initial stage of preparing the solid catalyst compound.
U.S. Pat. No. 4,387,045 to Sakurai et al. provides an olefin polymerization catalyst comprising a solid catalyst obtained by reacting an organomagnesium compound with a titanium or vanadium compound having at least one halogen atom. The solid catalyst is then reacted with an organometallic compound and an inorganic or organic aluminum, silicon, tin or antimony compound prior to the polymerization process. During polymerization, aluminum alkyl compounds are added to catalyst component as the sole co-catalyst system.
U.S. Pat. No. 4,431,571 to Karayannis discloses a comminuted, supported polymerization catalyst for alpha-olefins comprising an organoaluminum compound and a solid titanium-containing component formed by comminuting a solid reaction product comprising at least one halogen-containing compound of titanium (IV); at least one electron donor; and at least one hydrocarbon-insoluble, magnesium-containing compound; and retreating such comminuted product with at least one halogen-containing compound of titanium (IV); at least one haloalkyl-chlorosilane; and at least one organic acid ester. The solid catalyst component is then reacted with an organoaluminum cocatalyst during the polymerization of .alpha.-olefins.
U.S. Pat. No. 4,477,588 to Hawley relates to a catalyst which comprises the product obtained by reacting magnesium dihalide, 4-phenyl phenol, ethyl benzoate, and titanium tetra-n-butoxide. This solid product is then reacted with an organoaluminum halide comprising ethylaluminum sesquichloride followed by a mixture of halogen-containing mixture comprising titanium tetrachloride, trichlorosilane, and silicon tetrachloride. Hawley also discloses using the solid catalyst component described hereinabove in the polymerization of propylene by combining the catalyst with a triethylalumum cocatalyst.
U.S. Pat. No. 5,034,365 to Buehler et al. discloses a polymerization catalyst similar to that disclosed in patent '631 except that a second modifying compound having the structural formula SiH.sub.r X.sup.2.sub.s, where X.sup.2 is halogen; r is an integer of 1 to 3; and s is an integer of 1 to 3 with the proviso that the sum of r and s is 4, is added prior to the step of contacting the solid product with a first titanium-containing compound.